(1) Field of the Invention
The present invention concerns the assessment of the amount of releasable gas in a gas bottle containing compressed gas. In particular, the invention relates to apparatus for assessing the amount of releasable gas in a bottle when resting on a support therefor, by causing pivoting movement of the gas bottle.
(11) Description of the Prior Art
Bottles containing compressed and liquified low molecular weight hydrocarbons such as butane, isobutane, propane and mixtures thereof are commonly used as a source of gaseous heating and/or cooking fuel in mobile accommodation such as caravans and boats, where it is not possible or viable to connect the mobile accommodation to a mains supply. Recently, portable gas fires have been developed for more general use, which use a gas bottle containing compressed gas, the fire having a housing which defines a holder for the gas bottle itself.
When a compressed gas is contained in liquified form in a gas bottle, it is not possible easily and reliably to measure the amount of fuel remaining as releasable gas simply by using a pressure gauge, since a pressure gauge can measure only the partial pressure of gas above the liquid gas in the bottle and the partial pressure depends to a large extent on the ambient temperature, rather than solely on the amount of fuel left in the bottle. Accordingly, it is not until there is very little or no liquid gas left in the bottle that a pressure gauge will register a significant pressure drop to show that the bottle is becoming empty. By that time, however, there will be only a small amount of releasable gas, and the bottle can be expected to be exhausted after only a short period of further use.
It is possible to determine the amount of releasable gas still remaining in a bottle of compressed and liquified gas on the basis of weight, if both the weight of the gas charge itself and the initial weight of the gas charge and bottle are known. Because standard sizes of bottles are always charged with a constant amount of gas, if a full bottle is weighed before it is put into service, and then, when a user wishes to know how much gas remains, the bottle is weighed again, the remaining weight of gas can be calculated. This is done by subtracting the known weight of the initial gas charge from the first weighing, thus giving the empty bottle weight, and then the bottle weight is subtracted from the second weighing, giving the weight of the remaining gas. Since the weight of the initial gas charge should always be constant, the procedure would be simplified if the weight of all gas bottles of a certain size were constant, but unfortunately there are significant variations in empty bottle weights, expecially when compared to the weight of the initial gas charge.
The procedure described above is of course not particularly convenient for occasional use by a domestic user of bottled gas, especially when the bottle is located in an enclosure such as in a portable gas fire. The gas bottle has to be weighed before being put into service and the reading noted for later use; then when it is desired to know the amount of gas remaining, the bottle typically will have to be disconnected from the apparatus it feeds, lifted on to a suitable weighing machine and the reading noted and the bottle replaced and reconnected, whereafter the calculation has to be performed. Moreover, not many households have weighing machines suitable for weighing gas bottles, but not infrequently bathroom scales have been pressed into service when a weighing is to be performed.